Refractory bodies as fixed bed coal gasification diluents

ABSTRACT

The swelling of coal in fixed bed coal gasification is accommodated by the addition of a diluent to the charge of coal in approximately 1:1 volume ratio (or higher) in the form of strong, open-structured bodies. The structures described herein as diluent bodies are hollow refractory cylinders capable of retaining structural integrity throughout the profile of temperature exposure and having cavities large enough to accomodate the swelling of coal and add porosity to the bed.

United States Patent 1191 1111 3,811,849 Woodmansee 1 May 21, 1974 [54] REFRACTORY BODIES AS FIXED BED 2,662,007 12/1953 Dickinson 48/206 COAL GASIFICATION DILUENTS 2,341,861 2/1944 s 201/38 2,868,631 1/1959 Woebcke 48/206 [75] Inventory Donald E. Woodmansee,

Schenectady Primary Examiner-Robert L. Lindsay, Jr. [73] Assignee: General Electric Company, Assistant ExaminerPeter Kratz Schenectady, NY. Attorney, Agent, or Firm-Leo l. MaLossi; Joseph T. [22] Filed Dec 19 1972 Cohen; Jerome O. Squillaro 1 [2 Appl No 316,454 ABSTRACT The swellin of coal in fiited bed coal asification is 52 ..c1 4 4 g g 1 Us 8/202 35 65 accommodated by the addition of a diluent to the 51 Int. Cl. cio 3/16 charge approximately "(Mme (or [58] Field of Search U 205 higher) in the form of strong, open-structured bodies. 48/206 6 9 6 The structures described herein as diluent bodies are 1 hollow refractory cylinders capable of retaining struc- [56] References Cited tural integrity throughout the profile of temperature exposure and having cavities large enough to accomo- UNITED STATES PATENTS date the swelling of coal and add porosity to the bed. 3,463,623 8/1969 Forney 48/99 1,030,333 6/1912 Rusby et al. 48/203 4 Claims, 1 Drawing Figure C0141. D/LUENT r- COMBUSTION ZONE 7?: WASHER REFRACTORY BODIES AS FIXED BED COAL GASIFICATION DILUENTS BACKGROUND OF THE INVENTION Fixed bed coal gasifiers have been known and used and it has been recognized that successful operation thereof depends upon using non-caking coals or coke to accomplish the gasification. When care is not taken to limit the fixed bed composition in this way the swelling of the coal cuts off requisite bed porosity and thereby limits gas-solid contact.

In the fixed bed coal gasification process, as the coal enters the gasifier at the top and lands on the top of the charge, it receives heat from the upwardly moving product gas. As the combustion process near the bottom of the gasifier consumes some of the coal and the rest of the coal is gasified, coal at the top of the charge gradually moves down passing through a series of treatment stages: initial heating; devolatilization and coking; gasification, and carbon oxidation. A large number of chemical reactions occur and a, minimum temperature of about l,700 l,900F. is required. When air and steam are introduced to the combustion zone, the end product is called producer gas; when oxygen and steam are employed, the end product is called synthesis gas.

If the product gas is to be burned in a gas turbine, the erosive (particles of ash), corrosive (e.g. Na and K compounds) and ammonia must be'removed by washmg.

The object of this invention is to be able to utilize run-of-mine coal regardless of swelling and caking characteristics in fixed bed coal gasifiers. In contrast to fluid bed coal gasifiers, the fixed bed has definite advantages, primarily associated with the counter current movement of the product gas relative to the movement of the coal in the gasifier. More sensible heat remains in the gasifier instead of leaving with'the product gas and the coal is devolatilized before it is gasified enabling the volatiles to form part of the product gas.

' SUMMARY OF THE INVENTION This invention encompasses means for solvingthe problem of the swelling and caking of coal in the fixed bed gasification of coal wherein strong, openstructured bodies are distributed in the coal being charged to the gasifier. The ratio by volume of diluent bodies to coal should be at least about 1:1. Hollow refractory cylinders have been successfully demonstrated as diluent bodies in fixed bed coal gasification with strongly swelling coals.

BRIEF DESCRIPTION OF THE DRAWING This invention is illustrated by 'way of example in the accompanying schematic representation of a coal gasifier receiving a coal/diluent charge, the diluent being recycled.

DESCRIPTION OF THE PREFERRED EMBODIMENT The arrangement shown in the drawingis illustrative of the process of this invention employing shaped diluent bodies; namely, hollow refractory cylinders.

Such diluent bodies must have and must retain structural integrity throughout the temperature profile in order to provide a bed support to minimize crushing of the bed as these diluent structures move down with the bed during the process. The cavity in the diluent body must be large enough to accommodate swelling of the coal and also contribute added porosity to the bed to promote gas/coal contact. In addition, these refractory diluent bodies must be capable of surviving repeated cycling through the gasifier and transport apparatus.

Run-of-mine coal and refractory diluent bodies are deposited as a mixed charge into gasifier 10 via hopper 11 in the properproportions (e.g., 50 percent diluent by volume and 50 percent coal by volume). The layered charge shown has been found to be preferable to an intimately mixed charge. The coal plus diluent moves down to the combustion zone and the refractory bodies settle on grate 12 with the ash. Ash and refractory bodies are removed from grate 12 to drop into an ash lockhopper 13 from which they drop down on and are carried away by conveyor belt 14. At screen 16 the ash is separated from the refractory bodies, that are then carried back up to the feeding station for mixing with the coal.

The diluent bodies may be made of silicon carbide, alumina, zirconia, magnesia, etc. as long as the starting composition is sinterable and the resulting body has sufficient structural integrity. The cylinders shouldbe at least about two inches in length with an outer diameter of at least about 1 inches. The hole should provide significant cavity space and still leave sufficient wall thickness for the cylinder to retain strength. The hole should be at least about %-inch I.D.

Exemplary silicon carbide hollow cylinders were prepared from clay-bonded silicon carbide powder (Car bofrax No. 4 Castable or Ramming Mix Carborundum Co.). The powder was mixed with a small amount of water and compacted in a mold under about 10,000 psig in an'arbor press. There was no need to heat the bodies as directed in the instructions for the use of this material, since the bodies were strong enough to be charged with the coal and they were thereuponheated in the reducing atmosphere in the gasifier itself. The size bodies produced were two inches long with l /-inch OD. and ii-inch I.D.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In the process for generating a gas mixture containing combustible components wherein coal and a diluent material distributed relatively uniformly therethrough comprise a downwardly moving bed placed into gas exchange relationship with an upwardly moving gas mixture, the initial gaseous input at the bottom of said bed being steam and an oxygen-containing gas, the improvement comprising the step of employing as the diluent material a plurality of refractory bodies, said bodies being in the form of hollow cylinders retaining structural integrity throughout the profile of temperature exposure with the cavity in each body being large enough to accomodate swelling of said coal and to add porosity to said bed to promote gas-coal contact, the yohi rne raLio of refractory bodies to coal being at least about 1:1.

2. The improvement of claim 1 wherein the refractory material is silicon carbide.

3. The improvement of claim I wherein the hollow cylinder has an outer diameter of at least about 1% inches, an inner diameter of at least about three-fourths inch and a minimum length of at least about 2 inches.

4. The improvement of claim 1 wherein the refractory bodies are separated from the coal ash and recycled. 

2. The improvement of claim 1 wherein the refractory material is silicon carbide.
 3. The improvement of claim 1 wherein the hollow cylinder has an outer diameter of at least about 1 1/2 inches, an inner diameter of at least about three-fourths inch and a minimum length of at least about 2 inches.
 4. The improvement of claim 1 wherein the refractory bodies are separated from the coal ash and recycled. 